1. Field of the Invention
This invention relates, in general, to vibratory feeders and, in particular, to a control circuit with feedback for use with vibratory feeders for controlling the rate of feed of parts.
2. Description of the Prior Art
The control apparatus for vibrator feeders of the prior art comprises a silicon control rectifier (SCR) to rectify the A.C. line voltage applied to the solenoid of the vibrator feeder and to control the current flow through the feeder solenoid. The SCR blocks the current flow through the feeder solenoid, until a trigger pulse is applied to its gate, at which time the SCR is rendered conductive and remains conductive as long as a sufficient forward current is maintained. The SCR is triggered conductive during a positive half cycle of the current supplied to the feeder solenoid, and remains conductive for the remainder of the positive half cycle. The SCR is cut off for the negative portion of the cycle since it will not conduct reverse current. Triggering of the SCR is controlled by purely a bias control which is a A.C. phase shift voltage superpositioned by a D.C. bias voltage. The control bias voltage applied to the gate of the SCR varies the voltage output of the SCR to the solenoid. Of particular importance is that in the control apparatus of the prior art, this control bias voltage is adjusted by a simple, hand-adjustable, external potentiometer varied by the operator to suit his application.
The drawback of the above-described prior art device is that the output of the SCR is not regulated other than by the external potentiometer, as there is no feedback to supply information as to input line voltage fluctuations and/or output load variations. There has long been recognized a problem concerning wide fluctuations in a fixed amplitude setting of the prior art vibratory apparatus when frequently experienced line and/or load changes occur. Since the present state of the art recognizes only the utilization of a potentiometer to vary the control bias voltage to the SCR, the above-described inherent problems prevent effective use of vibratory apparatuses.
In view of the drawbacks suffered by the prior art vibratory apparatuses, it can readily be seen that there is a need in the part feeding industry for a vibratory apparatus which provides for output load regulation and/or input line regulation to prevent wide amplitude variation with A.C. line and/or output load variation.